The present invention relates to a casing scraper for cleaning the inside of a tubular member and more specifically for cleaning the interior surfaces of pipelines or oil, gas, or water well casings, tubes or pipes.
It is usual to ensure and maintain the physical integrity of a well bore hole by lining it with a casing, typically steel pipe, as it is drilled. This casing wall is cemented in place during completion of the drilling operation. This cementing operation leaves cement residue on the casing wall which must be removed before the well is put into production. Furthermore cleaning of the casing wall is necessary at intervals during well production to remove accumulated debris and residues, such as oil, paraffin and scale. Studies have demonstrated that debris and residues on the internal walls of the well casing have a negative impact on well productivity.
The standard tools used for cleaning casing walls are referred to as casing scrapers and are well known in the art. Typically a casing scraper comprises a cylindrical body having a plurality of scraper blades or wire bristles disposed at intervals around its outer surface, and a mandrel which facilitates connection to a drill string. In use, the casing scraper is mechanically driven through the well casing on the drill string, causing the scraper blades or bristles to scrape the inner surface of the well casing.
The casing scraper may be mounted towards the end of the drill string or at a point along its length depending on the region of the well casing which it is required to be used on.
It is known to improve the cleaning action of casing scrapers by circulating cleaning fluid down the drill string to the casing scraper. The cleaning fluid may exit the drill string at a point below the casing scraper to flow back around the exterior of the cleaning scraper, carrying with it debris and residues scraped from the wall of the well casing as it does so. Alternatively, the cleaning fluid may be directed under pressure through radially extending nozzles in the wall of the casing scraper to scour the wall of the well casing. Fluid circulation around the casing scraper causes debris and residues scraped from the casing walls to be carried to the surface of the well bore for removal.
Whilst the effectiveness of conventional casing scrapers varies from one design to another they all have in common that it is not possible to determine whether debris and residues arriving at the surface of the well bore in the cleaning fluid has been scoured from the particular region of the well casing which is actually subject to cleaning action. In this regard, it will be understood that the cleaning fluid circulating back to the surface of the well bore may pick up material which has been dislodged from the walls of the well casing above the casing scraper itself, as well as below it. This is unsatisfactory in that the well operator has no way of knowing whether the cleaning device is operating in an effective manner.
It is an object of the present invention to provide a casing scraper for cleaning the interior wall of a well casing which allows debris scoured from the wall of a well casing in the immediate vicinity thereof to be collected at will for subsequent inspection at the surface of the well bore.
According to the present invention there is provided a casing scraper for cleaning the interior wall of a well casing, comprising a generally cylindrical body defining an uppermost end adapted for connection to a drill string and having a plurality of scraping or scouring elements disposed around the outer surface thereof for contacting the interior wall of the well casing and a bore extending through the cylindrical body, one end of which bore is adapted for connection to a source of cleaning fluid and the other end of which bore is connected to a tail pipe extending below the lowermost end of the cylindrical body, which tail pipe has at least one opening in it through which cleaning fluid may be circulated into the well casing, wherein the casing scraper further comprises a filter located above the openings in the tail pipe and remotely operable means for selectively directing the flow of cleaning fluid from passing outside the filtration means to passing through the filtration means.
In a preferred embodiment of the present invention the filtration means is housed within the cylindrical body and forms an annulus around the bore extending therethrough. However, it may be housed separately from the cylindrical body, for example, on the tail pipe beneath the cylindrical body.
Conveniently, the means for selectively directing cleaning fluid to pass through the filtration means comprises a radially expandable element, such as a rubber plug, which is engageable with the casing wall to prevent fluid flow around the periphery thereof, which rubber plug has flow apertures therein through which cleaning fluid can pass into the filtration means. In normal use fluid takes the path of least resistance around the periphery of the rubber and little or no fluid passes through the filtration means. However, when the rubber plug is operated to block the fluid flow path around its periphery the fluid is forced to pass through the flow apertures and into the filtration means.
Conveniently, the rubber plug is annular and is mounted on the said tail pipe, above the apertures therein. Radial expansion of the rubber plug is achieved by compressing it between two plates which are operatively moveable relative to one another to reduce the distance therebetween. The relative movement may be achieved in a variety of ways. Preferably, one of the said plates is mounted on the lower end of the cylindrical body and the other is mounted on the said tail pipe, and the tail pipe is able to move longitudinally within the bore extending through the cylindrical body to shorten the distance between the plates.
Preferably, the rubber plug is rotatable relative to the tail pipe. This may be achieved by providing bearings between the rubber plug and the tail pipe. This allows the drill string and the tail pipe to be rotated in the well casing even when the rubber plug is radially compressed to engage with the interior wall of the well casing. Rotating the drill string and the tail pipe causes turbulence within the fluid and greatly improves the cleaning action thereof.
Rotary movement of the drill string is particularly beneficial in wells that are not vertical. Here, the drill string lays against the walls. If chemicals are pumped and the drill string is stationary the chemicals cannot contact the side of the casing against which the drill string rests. If, however, the drill string is rotated during pumping the rotary action carries the chemicals into contact with the casing wall and aids the cleaning operation.
Preferably, the tail pipe is connected to the cylindrical body in such a way as to permit relative movement thereof on a longitudinal axis but to prevent relative rotational movement thereof. Conveniently this may be achieved by providing a key on the tail pipe which is slidably within a longitudinally extending keyway in the cylindrical body, or vice versa.